Known in the art is a process for producing an acid agent which comprises condensation of phenol with an aldehyde at a temperature within the range of from 85.degree. to 100.degree. C. for a period of several hours, followed by sulphonation of the resulting novolac with sulphuric acid at a temperature of 100.degree.-110.degree. C. for 2-6 hours (cf. British Pat. Nos. 1,361,045; 1,359,683).
This prior art process has a disadvantage residing in intermittent character of the process, long duration of the technological cycle, considerable power input and labour consumption.
The resulting acid agent also has disadvantages such as a high viscosity of the sulphonated novolac, presence of sulphuric acid, sometimes in substantial amounts, therein; a low content of phenol rings, unsubstituted with sulphoxy group, capable of performing the function of an active acceptor of formaldehyde. To lower the viscosity, such as acid agent should be diluted with water which increases its corrosion activity.
Known in the art is a process for producing an acid agent which is carried out in a batch reactor in two stages: at the first stage phenol is reacted with sulphuric acid at a temperature of from 125.degree. to 150.degree. C. for a period of 0.5 to 1.0 hour; at the second stage the product resulting from the first stage is reacted with formaldehyde at a temperature within the range of from 30.degree. to 50.degree. C. for 1-2 hours (cf. British Pat. No. 1,283,113).
This prior art process has disadvantages residing in a intermittent character thereof, substantial power consumption assotiated with the necessity of intensive stirring.
The acid agent produced by this process is a relatively weak acceptor of the aldehyde liberated upon curing of a phenol-aldehyde resole and imparts an increased corrosive activity to the phenol-aldehyde resins cured thereby.
Also known in the art is a process for producing a phenol-aldehyde formed plastic with the use of an acid agent as a catalyst which comprises a condensation product of sulphonated phenol, a nitrogen-containing organic compound pertaining to the class of amines or amides, and formaldehyde.
Said acid agent is prepared by the process involving reaction of sulphuric acid, phenol, the nitrogen-containing compound and the aldehyde in a batch reactor in three stages. At the first stage phenol is reacted with sulphuric acid at a temperature within the range of from 80.degree. to 100.degree. C. for a period of from 2 to 24 hours; at the second stage sulphonated phenol is reacted with the nitrogen-containing compound at a temperature of from 40.degree. to 70.degree. C. for 0.5-1.0 hour; at the third stage the resulting product is reacted with the aldehyde at a temperature within the range of from 40.degree. to 70.degree. C. for 0.25 hour (cf. British Pat. Nos. 1,228,857 and 1,272,857). This prior art process has disadvantages residing in its intermittent character, long duration of the technological cycle, as well as considerable labour and power consumption.
The nitrogen-containing compound incorporated in said acid agent lowers the corrosion activity of cured phenol-aldehyde resins and also behaves as an acceptor of the aldehyde evolved upon curing of the phenol-aldehyde resole.
The acid agent as used in this prior art process also has disadvantages, for example, insufficient strength and brittleness of phenol-aldehyde resins cured thereby. Furthermore, this acid agent is liable to crystallization at a low temperature which in certain cases causes substantial technological difficulties.
Consequently, all prior art process for producing an acid agent have the following basic disadvantages: PA1 intermittent character of the process resulting in: PA1 losses of both the starting materials and the final product; PA1 long duration of technological cycle; PA1 considerable power and labour consumption.